Nail matrix melanoma in adolescents and young adults: a retrospective dermoscopic study.
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BACKGROUND: Nail matrix melanoma (NMM) is a rare subtype of melanoma, accounting for approximately 2-3% of all melanoma cases. Its incidence ranges from 0.3-1.5% in White populations to up to 20% in African and Asian populations. While more common in older adults, its occurrence in patients under the age of 30 years is exceedingly rare. This rarity often leads to delays in diagnosis, particularly in adolescents and young adults presenting with longitudinal melanonychia. OBJECTIVES: To characterize the clinical, dermoscopic and histopathological features of NMM in patients aged 40 years or younger and to raise awareness about the occurrence of melanoma in this rarely affected age group. METHODS: We retrospectively reviewed all histopathologically confirmed cases of NMM diagnosed at our institution between 2015 and 2025. Patient demographics, clinical presentation, dermoscopic patterns, histological findings and follow-up data were analysed. Nail unit biopsies were performed in a multidisciplinary setting involving a nail surgeon and two dermatopathologists. RESULTS: Fifty-nine patients were diagnosed with NMM, of whom 25 (42%) were aged ≤ 40 years, including 15 patients under 30 years. All patients under 30 years had melanoma in situ. Among the ≤ 40-year age group, 22 (88%) had melanoma in situ and 3 (12%) had invasive melanoma, with a mean Breslow thickness of 1.0 (range 0.7-1.4) mm. Dermoscopy revealed irregular longitudinal lines in 96%, three or more colours in 65%, and disruption of parallelism in 74% of lesions. Spiral melanonychia, a pattern commonly linked to benign naevi, was observed in 26% of cases. In eight patients, serial dermoscopy revealed progressive changes that triggered biopsy. In seven patients, the initial biopsy yielded a nonmalignant or indeterminate diagnosis, and melanoma was confirmed only after progression prompted re-biopsy. Comparative analysis with 64 age-matched patients with nonacral, nonmucosal cutaneous melanomas showed a higher proportion of in situ disease among patients with NMM. CONCLUSIONS: NMM can also occur in adolescents and young adults - an age group in which it is often under-recognized. Despite most cases being diagnosed at an early (in situ) stage, delays in diagnosis are common. Clinicians should maintain a high index of suspicion for solitary, atypical longitudinal melanonychia developing after puberty to improve diagnostic accuracy and patient outcomes.